1. Technical Field
The present invention relates to fibers having self-crimping characteristics, wherein the fibers are composed of two or more polymers of differing viscosities, and corresponding methods for producing such self-crimping fibers.
2. Description of the Related Art
Woven and non-woven fabrics and yarns having desirable qualities can be manufactured from crimped side-by-side, bicomponent synthetic polymer fibers. Such bicomponent fibers typically include two different polymers arranged as microfilaments or segments across the transverse cross section of the fiber, which segments extend continuously along the length of the fiber. A melt spinning process involving extrusion of the molten polymer from orifices of a spinneret can be used to form these side-by-side bicomponent fibers. By causing one or both of the constituent segments to crimp after extrusion, a fine denier fabric or yarn can be produced with improved characteristics, such as greater bulkiness and softness, superior flexibility and drape, and better barrier and filtration properties for use in products such as disposable absorbent articles, medical garments, filtration materials, apparel, and carpet.
It is well known in the art to produce certain bicomponent fibers having the ability to crimp based upon different thermal shrinkage and/or strain characteristics. For example, U.S. Pat. No. 5,093,061 to Bromley et al., the disclosure of which is incorporated herein by reference in its entirety, discloses melt spinning sub-streams of incompatible polymers having significantly different thermal shrinkage characteristics, such as nylon and polyethylene terephthalate (PET), to incorporate a latent helical crimp into the extruded fiber. Additionally, it is known to manufacture self-crimping polyester fibers by melt spinning polybutylene terephthalate (PBT) and PET in a side-by-side manner. The PBT/PET fiber typically exhibits desired crimping characteristics due to the PBT side becoming crystalline while the PET side remains amorphous thus establishing a strain differential between the two components during drawing of the fiber after extrusion. Methods such as these for providing self-crimping fibers are typically disadvantageous because of the increased material and/or manufacturing costs associated with providing two or more different polymers having suitably different physical properties to induce crimping.
Other processes are known in the art for inducing crimping characteristics in bicomponent fibers including two or more of the same polymers. However, those processes typically require manufacturing steps that are complex and require considerable expense for mass production of the self-crimping fibers. For example, U.S. Pat. No. 4,522,773 to Menezes et al., the disclosure of which is incorporated herein by reference in its entirety, discloses a process for producing self-crimping polyester yarns having the same-polymer components, wherein the process includes extruding a plurality of molten streams of polyester at different extrusion speeds and combining the streams to form thick and thin regions in the combined streams out of phase with each other. The combined streams are then quenched and transformed into solid filaments, passed through a conditioning zone provided with a gaseous atmosphere at a temperature sufficient to produce filaments exhibiting a desired yarn shrinkage and wound at a substantially constant wind-up speed. Menezes is limited in that the process requires a significant modification to the fiber forming equipment to ensure that polymer components achieve differing extrusion velocities prior to combining with each other.
Another known process of forming self-crimping fibers utilizing the same-polymer components is disclosed in U.S. Pat. No. 3,718,534 to Okamoto et al., the disclosure of which is incorporated herein by reference in its entirety. The Okamoto et al. process discloses the combination of two or more of the same-polymer components in the core of a sheath/core melt extruded filament, wherein the same-polymer components have different heat shrinkage or elongation properties. Upon extrusion of the polymer components as the core within a second polymer sheath, the second polymer sheath is removed by dissolution in a solvent to expose the core portion filament. The resultant filament is further processed, e.g., by heating or stretching, to induce crimping. The Okamoto et al. process is limited in that the manufacturing step of providing and subsequently removing a sheath to form the finished fiber increases production costs considerably.
A process for producing a side-by-side self-crimping fiber having the same-polymer components is highly desirable due to the reduced costs associated with obtaining the raw material components. However, attempts at obtaining such fibers without substantial modification to conventional fiber production equipment and/or processing steps (e.g., the processing steps required in Menezes et al. and Okamoto et al.) have typically met with failure. For example, the production of a side-by-side PET/PET self-crimping fiber utilizing conventional melt spinning techniques has been unsuccessful due to the side-by-side PET components exhibiting similar physical properties during fiber production. Both side-by-side PET portions remain amorphous during drawing of the fiber after extrusion which prevents the formation of a stable fiber crimp.
It is therefore desirable to provide a self-crimping fiber having two or more of the same polymer components (e.g., PET/PET) that exhibits a desirable and stable crimp and maybe easily and economically manufactured.
Therefore, in light of the above, and for other reasons that become apparent when the invention is fully described, an object of the present invention is to produce self-crimping fibers utilizing two or more of the same-polymer components without the need for additional complex or expensive manufacturing steps.
Another object of the present invention is to manufacture self-crimping fibers from two or more of the same-polymer components and having a desirable crimp stability. A further object of the present invention is to produce yarns, fabrics and other textile products having improved characteristics from self-crimping fibers including two or more of the same-polymer components.
Yet another object of the present invention is to produce a multicomponent fiber utilizing at least two of the same-polymer components wherein a suitable crystallinity differential develops between at least two components during formation of the fiber to induce a stable crimp in the fiber.
The aforesaid objects are each achieved individually and in combination, and it is not intended that the present invention be construed as requiring two or more of the objects to be combined unless expressly required by the claims attached hereto.
In accordance with the present invention, the previously noted difficulties in forming a self-crimping fiber with same-polymer components is overcome by establishing an effective crystallinity differential between at least two of the polymer components that induces a stable crimp in the fiber prior to being subjected to a final heat setting treatment. The crystallinity differential between the two polymer components is typically achieved by selecting a suitable viscosity differential between at least two of the same-polymer components in combination with selecting a suitable geometry of the two components with respect to each other as the components are extruded through a spinneret hole. The geometries of the polymer components are typically configured such that higher viscosity polymer components of the fiber have transverse cross sections that are relatively thin and flat and have high perimeter-to-area ratios. Preferably, the transverse dimensions of the polymer components having differing viscosities are selected so that the higher viscosity polymer components have greater perimeter-to-area ratios than that of the lower viscosity polymer components.
A self-crimping fiber manufactured according to the present invention (e.g., a side-by-side PET/PET fiber) will exhibit stable crimping characteristics similar to self-crimping fibers produced with two or more different polymer components (e.g., PET/PBT). Additionally, a self-crimping fiber of the present invention can be formed into yarns and fabrics with superior characteristics, such as greater bulkiness and softness, superior flexibility and drape, and better barrier and filtration properties for use in products such as disposable absorbent articles, medical garments, filtration materials, apparel, and carpet.
Thus, self-crimping fibers manufactured in accordance with the present invention overcome the previously noted difficulties in obtaining stable crimping fibers having two or more of the same-polymer components. The fibers of the invention maybe manufactured utilizing the same-polymer components, thereby reducing material costs and additional manufacturing steps.
The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following definitions, descriptions and descriptive figures of specific embodiments thereof wherein like reference numerals in the various figures are utilized to designate like components. While these descriptions go into specific details of the invention, it should be understood that variations may and do exist and would be apparent to those skilled in the art based on the descriptions herein.